Method and device for controlling the operating temperature of a hydraulic operating medium of a drive unit of a vehicle

Abstract

In a method for controlling the operating temperature of a hydraulic operating medium for a drive unit of a vehicle in a selected range, the operating temperature is controlled by controlling the volume flow of the operating medium for a heat exchange between the operating medium and a secondary heat transfer medium flow medium to a predetermined desired value as a function of the actual value of the operating temperature and as a function of at least one other vehicle parameter, by which a certain temperature influencing effect on the operating medium can be provided. The selected range of the operating temperature includes both the temperature values occurring in the warm-up phase of the drive unit and temperature values, which are substantially higher than the desired value.

1. A method of controlling the operating temperature of a hydraulic operating medium of a drive unit of a vehicle, said method comprising the steps of controlling the operating temperature of the hydraulic operating medium by controlling, in a warm-up phase of the drive unit, the volume flow per unit time of the operating medium in heat exchange with a secondary flow medium, which is used as heat transfer medium, as a function of the operating temperature of the hydraulic operating medium and the secondary flow medium in such a manner that the flow of the hydraulic operating medium, which is subjected to heat exchange, is set to zero, as long as the temperature of the hydraulic operating medium is higher than the temperature of the secondary flow medium, and is set toward a maximum—when the temperature of the hydraulic operating medium is lower than the temperature of the secondary flow medium. 
     
     
       2. A method according to  claim 1 , wherein the setting of the operating temperature to a predetermined desired value takes place under temporary suppression of the heat exchange for a variable partial amount of the volume flow of the operating medium. 
     
     
       3. A method according to  claim 2 , wherein the same secondary flow medium is used for the heat exchange during the warmup phase of the drive unit and at operating temperatures above the desired value. 
     
     
       4. A method according to  claim 1 , wherein the setting of the operating temperature to a predetermined desired value is accomplished by automatic temperature control means. 
     
     
       5. A method according to  claim 4 , wherein the operating temperature is controlled to a predetermined desired value additionally as a function of the gradient of the operating temperature of the operating medium. 
     
     
       6. A method according to  claim 1 , wherein the volume flow of the operating medium, which flow is subjected to the heat exchange, is set to a maximum—if the operating temperature of the operating medium is smaller than a minimum value of the operating temperature of the secondary flow medium. 
     
     
       7. A method according to  claim 6 , wherein the minimum value of the operating temperature of the secondary flow medium lies in the temperature range of between 60° C. and 110° C. 
     
     
       8. A device for controlling the operating temperature of a hydraulic operating medium for a drive unit of a vehicle including a heat exchanger for adjusting the operating temperature of the hydraulic operating medium, a control valve for controlling the volume flow per unit time of the hydraulic operating medium through the heat exchanger for heat exchange between the hydraulic operating medium and a secondary flow medium to a predetermined desired value as a function of at least one of the operating temperature and another vehicle parameter, a bypass line bypassing the heat exchanger said control valve having a valve housing with a first valve connection connected to an operating medium supply line, a second valve connection connected to said heat exchanger, and a third valve connection connected to said bypass line, a valve actuator arranged moveably in the valve housing for establishing selectively communication between said first valve connection and said heat exchanger on one hand, and a bypass line leading directly to a collecting tank of the drive unit, on the other hand, said valve actuator including a temperature sensitive control element for switching the valve during the startup phase of the motor vehicle such that the hydraulic operating fluid is directed through the line bypassing the heat exchanger when the temperature of the secondary fluid in the heat exchanger is lower than the temperature of the hydraulic operating fluid or higher by only a predetermined amount but directs the hydraulic operating fluid through the heat exchanger for heat exchange with the secondary fluid when the temperature of the secondary fluid exceeds the temperature of the hydraulic operating fluid in order to raise the temperature of the hydraulic operating fluid during the startup phase as rapidly as possible. 
     
     
       9. A device according to  claim 8 , wherein said heat exchanger is connected to said second valve connection of said control valve by an inlet line for said operating medium, said heat exchanger having an outlet line for said operating medium providing for a direct connection between one of the heat exchanger, a collecting tank for the hydraulic operating medium and hydraulic medium consumers of the drive unit. 
     
     
       10. A device according to  claim 8 , wherein said control valve is a three-two-way directional control valve. 
     
     
       11. A device according to  claim 8 , wherein said control valve is a flow volume control valve. 
     
     
       12. A device according to  claim 8  including an electronic control unit which has at least one input for actual values of the operating temperature and inputs for actual values of other vehicle parameters, and an output for a control signal, which is formed from a desired value and at least one of the actual values for setting the operating temperature, and in which said control valve is provided with an electromotive valve actuating unit, which is connected to said output for operating an actuator of said valve, said electromotive valve actuating unit of said control valve being an electromagnet. 
     
     
       13. A device according to  claim 12 , wherein at least one of a temperature sensor for measuring the actual value of the operating temperature of the operating medium and the electronic control unit is arranged in a collecting tank for the operating medium. 
     
     
       14. A device according to  claim 8 , wherein the temperature-sensitive control element is a shape memory spring. 
     
     
       15. A device according to  claim 8 , wherein the temperature-sensitive control element is a bimetal spring. 
     
     
       16. A device according to  claim 8 , wherein the temperature-sensitive control element is an expansion element. 
     
     
       17. A device according to  claim 8 , wherein said valve is a spool valve and said valve actuator of said control valve is an axially movable control slide. 
     
     
       18. A device according to  claim 8 , wherein said supply line for the operating medium is connected to a feed pump and a pressure regulating valve.